The invention relates to a system and a method for transmitting OPC data via data networks, in particular the Internet, using an asynchronous data connection.
OPC (OLE for process control) is understood to mean a standard and manufacturer-independent specification of a software interface between Windows applications and automation systems, in particular for production control and automation, which permits the flow of data between an extremely wide range of systems, applications and devices without problems. OPC therefore represents a connection among process control, statistical production control, process optimization, other production applications, for example applications for carrying out production or for the production management, the corresponding real-time devices and Windows applications. For this purpose, it offers a series of OLE or COM-based standard interfaces and further adapted interfaces.
With the aid of data networks, it is possible to establish a data connection to a server from any desired computers, clients, as they are known, which have access to these data networks. This applies in particular to the World Wide Web (WWW), which is also called the Internet. The terms Web or Internet server or Web or Internet client, used in the following text, are used to illustrate the membership to the specific data network comprising the Internet, but in functional terms make no distinction from the meaning of the terms client and server which are used for all possible data networks. In the following text, the terms OPC client and OPC server will be understand to mean those computers which can additionally process data in the OPC data format. In the following text, when only the term client or server is used, this is understood to mean an OPC client or OPC server.
In the Internet, a data connection is established to what is known as a Web or Internet server. The access to an Internet server is carried out, for example, with the aid of known Internet browsers, for example Internet Explorer from Microsoft or Netscape Communicator from Netscape. When a data connection is being established from a Web or Internet client, as they are known, a request is output to an Internet server by entering and dispatching what is known as a URL address. When a data connection is established, the Internet server called answers with what is known as an HTML page (HTML=Hyper Text Markup Language), also called a Web page. The Web clients, as they are known, communicate with the Web servers by transport protocols. Each data connection between Web client and Web server is therefore based on a request protocol and, as a reaction to this, a response protocol.
Internet connections permit fast data interchange between locations which are physically widely separated. In conjunction with the OPC technology, it is thus possible for extremely different systems, applications and devices which can be located physically very widely removed from one another, to communicate with one another simply and quickly. Until now, however, it has not been possible to connect the full functional scope of the OPC technology to the Internet, since for this purpose an asynchronous data transmission method, that is to say time-independent, bidirectional communication, would be necessary, which has hitherto not been possible in the Internet.